Aggressive motivation and reinforcement in the Siamese fighting fish (Betta Splendens)

Abstract

This thesis describes operant behaviour rewarded by aggressive display in Betta splendens. Withdrawals during the encounters were related to the phase of the nest-building cycle, although not to the presence of the nest. Subordinates elicited more withdrawals than displaying males. Withdrawal is here interpreted as courtship, which was inhibited if the partner displayed aggressively, and sex discrimination in Betta splendens is discussed. Measures of behaviour during reinforcement were correlated with one another and with behaviour between reinforoements. One group of post-reward behaviour patterns delayed further operant responses. During reward, some behaviour patterns (e.g. attack, air gulping) ware associated with short, and others (e.g. lateral display) with long operant latencies. With the exception of air gulping, these relations could be accounted for in terms of relations to post-reward behaviour patterns. A second group of post-reward behaviour patterns, negatively related to the first, did not delay operant performance and was positively related to attack during reinforcement. Priming with aggressive display changed behaviour during the reward and decreased operant latency. This could not be accounted for by changes in post-reward behaviour. Increasing the interval between stimulus presentations (IPI) decreased attack and increased lateral display duration. Attack decreases operant latencies, but the existence of a latent period in turn reduces attack (the mechanism involves decay of stimulus induced excitation in the period when the stimulus is absent, i.e. the inter-reward interval). Two procedures which increase this interval decreased response rate : a time-out of 30 or 60 mins. after training reduced the number of responses in extinction by 50% approximately, whilst a fixed ratio (PR) schedule reduoed response rate and eliminated the intra-session acceleration in responding which occurred under continuous reinforcement. In a free-behaviour situation with food-rewarded doves, meal size first increased and then decreased as PR was increased. (Body weight was maintained by changes in feeding efficiency and meal frequency). Accompanying the meal-size changes, there were changes in anticipatory feeding (changes in the correlation between meal size and the post-meal interval) and in an index of intra-meal facilitation of feeding. Many of these effects depended on facilitatory effects of feeding which decayed during the inter-reward interval. Increasing PR size increased this interval, and reduced persistence in meals.